Pulmonary Functions and Health-Related Quality of Life among Silica-Exposed Workers.

BACKGROUND
This study aimed to investigate the pulmonary functions of silica-exposed workers and their health-related quality of life in an insulator manufacturing industry.


MATERIALS AND METHODS
In this cross-sectional study, participants selected from the manufacturing unit (n = 127) constituted the exposed group and those from the administrative department (n = 30) constituted the unexposed group. All subjects were evaluated using personal air sampling of crystalline silica, pulmonary function tests, and a quality of life questionnaire (36-item short form health survey [SF-36]).


RESULTS
The mean (SD) concentrations of crystalline silica were 0.507 (0.23) mg/m3 and 0.0116 (0.008) mg/m3 for the exposed and unexposed groups, respectively. All the pulmonary function indices and all the physical and mental health domains of the workers were significantly lower than those of the administrative clerks (p < 0.05). The silica concentration did not significantly correlate with the quality of life components and all the pulmonary function indices (p > 0.05), except for forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) (p < 0.05).


CONCLUSION
In conclusion, the workers exposed to higher levels of crystalline silica had lower values of pulmonary function indices and lower health-related quality of life; however, further follow-up studies are needed to confirm these findings.


INTRODUCTION
Occupational respiratory diseases rank among the most common occupational diseases, and are usually latent for a long time; hence, the disease is diagnosed during the final stages, when therapeutic measures are usually ineffective (1). Several acute and chronic pulmonary diseases are caused by inhaling hazardous chemical agents at the workplace, including dust and toxic particles, metal fumes, gases and vapors, and other air-borne pollutants (2).
Among them, the mineral dust contains various compounds and can cause various pulmonary diseases, depending on the individual affected (3,4). Silica is regarded as one of the most important minerals with different industrial uses, such as in the casting process, preparation of detergent powder, and grinding process, and as a raw material for manufacturing insulators, tiles, and ceramic (5,6). Mohammadi H,et al. 61 Tanaffos 2017; 16 (1): [60][61][62][63][64][65][66][67] The insulator manufacturing industry is associated with a risk of silica emission and its consequences. An insulator is a device that has a high electrical resistance and is used as a good electrical insulation between two conductors with different voltage levels; it may also be used between a conductor and the earth. Several countries, such as the United States, China, Spain, and Iran produce these silicon insulators and their employees are exposed to the air-borne pollution that results from milling, mixing, pressing, assembling, cutting, grinding, and extruding the equipment during its production process. Silicon is needed to strengthen the insulator substrate (7). reported that respiratory complaints in the silica-exposed group were significantly higher than in the unexposed group; moreover, the spirometry indices of the exposed group, except for FEV1/FVC, were significantly lower than those of the unexposed group (11).

TANAFFOS
Health-related quality of life is a multidimensional concept that includes the functional ability and mental health of a person; it is influenced by various factors, including physical/mental status, economic circumstances, personal beliefs, and individual-environment interactions (12). Occupation is a key factor affecting the health-related quality of life (13). Occupational environments consist of physical, mental, and social stimuli, each of which may be regarded as a stress factor (14). These stresses have detrimental effects on both physical (its health and function) and mental health (15). Considering the poor work conditions in the factories of developing countries, the routine life of workers may be adversely affected by environmental factors in various aspects, such as physical, mental, social, and economic. Hence, the concept of healthrelated quality of life becomes significant in these people (16).
The effects of occupational silica exposure on the pulmonary function have been reported in many studies (17); however, health problems, such as respiratory impairments, may be associated with a worse quality of life, and there are few studies that consider it in silicaexposed workers. Silicosis is an irreversible disease and is caused by exposure to free silica. Silicosis can lead to a reduction in the lung function of the exposed workers and interferes with their activities of daily living and work (18).
Consequently, it leads to a decline in their quality of life; however, there are few studies that evaluate the effect of the silica exposure and lung function on the quality of life of the workers (18). Therefore, the present study aimed to investigate the pulmonary functions and the health-related quality of life of silica-exposed workers in an insulator manufacturing industry, to help in developing programs that enhance the level of health in the workers of this industry.

Participants
This cross-sectional study was conducted among the workers in the manufacturing workshops (the exposed group) and the administrative department (the unexposed group) in one of the insulator factories in Saveh, Iran. Since the number of unexposed subjects was lower than the exposed subjects, to enhance the power of the study, the ratio of exposed to unexposed participants was considered to be 4. This ratio corresponded to the maximum power achievable by the study. Assuming α = 0.05, 1 -β = 0.80, and the effect size = 0.50, the sample size was calculated to be 157, in which 127 subjects belonged to the exposed group and 30 subjects to the unexposed group. G*power software (version 3. Germany) was used for the sample size calculation (19,20).
The participants were selected using a simple random method from the employees who are non-smokers and had been employed for at least five years and did not have any respiratory diseases, such as sinusitis, asthma, infection of

Measurement of silica concentration
Air sampling of crystalline silica was performed

Pulmonary function tests
The pulmonary function tests were performed to evaluate the capacity and volume of the lungs among the participants. Spirometry measurements, including FVC, were requested to discontinue drugs that might affect the respiratory system 24 hours before the test. In addition, all participants were trained before the spirometry test (10,22). The spirometry data were analyzed by comparing the obtained values to the predicted values. For a normal spirometry, the FVC and FEV1 should be equal to or greater than 80% of the predicted value, and the FEV1to-FVC ratio should be no more than 8-9 absolute percentage points below the predicted ratio (23).

Health-related quality of life assessment
The assessment of health-related quality of life was and Physical Component Summary (PCS). Using these two components, general health examination was conducted with using fewer items and the results interpreted.
Physical measures include items PF, RP, BP, GH, and the mental measure, which included items MH, RE, SF, and VT (26). The validity and reliability of the Iranian version of the questionnaire were approved by a previous study (27).

Statistical analysis
The  Table 1 presents the comparison of the mean (SD) demographic characteristics between the exposed and unexposed groups. Of the 157 subjects who participated in this survey, 127 were selected from the manufacturing unit (the exposed group) and 30 from the administrative department (the unexposed group); the mean (SD) ages were 39.28 (4.51) years and 39.03 (8.6) years for the exposed and unexposed groups, respectively. In the statistical analyses, there were no significant differences between the two groups in terms of demographic characteristics, including age, duration of employment, height, and weight (P>0.05; Student's t-test). The prevalence rates of all respiratory symptoms were higher in the exposed group, compared to the unexposed group; however, dyspnea and cough alone showed statistical significance (p < 0.001; chi-square test).

RESULTS
The mean (SD) crystalline silica concentrations were 0.507 (0.23) mg/m 3 and 0.0116 (0.008) mg/m 3 for the exposed and unexposed groups, respectively. The mean difference between the two groups was statistically significant (p < 0.001); moreover, the workers of the manufacturing unit were exposed to concentration excursions higher than the threshold-limit value -time- The results of spirometric testing (Table 2) showed that there were significant differences between the spirometry parameters of the two groups (p < 0.05); all the pulmonary function indices of the workers were significantly lower than those of the administrative clerks.

DISCUSSION
In the present study, the spirometric indices and health-related quality of life were compared between the workers who were exposed to silica dust and the employees of the administrative department in an insulator manufacturing industry. The results of air monitoring suggested that the levels of crystalline silica emission from the process units were approximately 20 times higher than the threshold-limit value -timeweighted average. These findings imply that there might be an increased risk of respiratory disorders and health problems for workers in response to silica dust exposure.
The mean spirometric indices of the group exposed to high levels of silica dust were statistically significantly lower than those of the unexposed group. In addition, the exposed workers showed a higher prevalence of respiratory symptoms. Sakar et al. found that the workers of ceramic factories, who were exposed to silica dust, had higher pulmonary signs, including cough, mucus, and shortness of breath, in comparison to the non-exposed ones Since routine spirometry was used to test the lung function of the study subjects and it is well known that silica itself primarily affects the lung diffusion capacity.
Further complementary studies may be performed using the diffusing capacity of the lung for carbon monoxide, besides spirometry (32). This may be important to detect early stage silica-related interstitial changes related to the reportedly high exposure levels.
No significant differences were observed between the two groups for the demographic variables; moreover, there were no air-borne contaminants with potentially damaging effects on the respiratory system and values higher than the TLV according to the reports of the health, safety, and environment sections of the factory studied; hence, conclusions on the potential reasons for the reductions in lung function parameters were evident.
Any health problem, especially pulmonary disorders that can cause a disruption in the normal life, can have a substantial impact on the quality of life (33). Based on the obtained results of the present research, the mean scores of all domains of the health-related quality of life in the exposed group were significantly lower than those of the unexposed group, and the lowest mean score in the

CONCLUSION
In general, the results showed that the workers who

Conflict of interest
The authors have no conflict of interest to declare.